1. Field of the Invention
The present invention generally relates to a notification technique for suitably notifying a line failure occurred in a line connection between a network apparatus and a terminal apparatus. More specifically, the present invention is directed to a line failure notifying apparatus capable of simply notifying an occurrence of a line failure to a terminal apparatus.
2. Description of the Related Art
In a system constructed of a network apparatus and a terminal apparatus, the below-mentioned two line failure recognizing methods by the terminal apparatus are conceivable:
(1) When the network apparatus detects a line failure, the network apparatus changes a signal state of a connection interface signal between the network apparatus and the terminal apparatus based on this line failure information. Accordingly, the terminal apparatus recognizes this line failure.
(2) A line failure is recognized by an upper layer of a communication protocol, for example, a session is interrupted, and a protocol fail among the terminal apparatuses.
Among the above-described recognitions, the recognition methods (1) is capable of recognizing the line failure within a short time period. Normally, the network apparatus fixes a data stream to such a data stream having all values of xe2x80x9c1xe2x80x9d with respect to a lower grade unit when the line failure is detected. However, since there are some possibilities that a data stream having all values of xe2x80x9c1xe2x80x9d is transmitted from a terminal apparatus on the transmission side, there are many cases that this information could not be directly used to notify the line failure.
Referring now to drawings, the above-described operations will be described.
FIG. 2 shows a basic idea to detect a line failure. FIG. 3 represents such a case that although a network system is operated under normal condition, this condition is erroneously recognized as a line failure.
Network apparatuses (TDMa and TDMb) own line interfaces (NP) and terminal interfaces (LS) as interfaces A control line (CL) is provided between the network apparatuses, independent from a data line (DL). Now, when a failure happens to occur in the line between the network apparatuses, the line interface (NP) of the network apparatus (TDMb) of the reception side detects the line failure, and fixes all values of a data stream into values of xe2x80x9c1xe2x80x9d, which has been received via the data line (DL).
In such a case that a bit stream having, for example, 64 bits of xe2x80x9c1xe2x80x9d is continuously detected in the terminal interface (LS) of the network apparatus (TDMb), the terminal interface (LS) recognizes this data stream as the line failure to execute a predetermined process operation. In this case, a predetermined process operation involves that in the case of the V.35 protocol by the CCITT rule, xe2x80x9cCDxe2x80x9d is set from an ON state to an OFF state, and in the case of the X.21 protocol, xe2x80x9cIxe2x80x9d is set from an ON state to an OFF state.
However, in such a case that such a signal whose bits exceeding 64 bits become accidently and continuously xe2x80x9c1xe2x80x9d is received via the control line (CL) of the network apparatus TDMa, the terminal interface (LS) of the network apparatus (TDMb) would recognize this bit stream as the line failure, although the data line (DL) is operated under normal condition. As a result, the above-described failure processing operation would be executed.
Therefore, in order to prevent such an erroneous error detection, as indicated in FIG. 4, when the terminal interface (LS) of the network apparatus (TDMa) receives the data having the bit stream exceeding 64 bits and the all values of xe2x80x9c1xe2x80x9d, the following process operation is carried out. That is, the bits of this data (bit stream signal) are inverted every 5 bits. As a result of such a bit inverting operation, since the signal transmitted between the network apparatuses (TDMa) and (TDMb) becomes such a signal having a bit stream of xe2x80x9c111101111011110xe2x80x94xe2x80x9d, the line interface (NP) of the network apparatus (TDMb) on the reception side does not recognize this bit stream as the failure. When this bit stream signal is outputted from the network apparatus (TDMb), the bits which have been inverted in the terminal interface (LS) are returned to the original values thereof, and then this bit stream signal is outputted as a bit stream signal of xe2x80x9c111111111111111xe2x80x94xe2x80x9d from the network apparatus TDMb.
However, as represented in FIG. 5, when such a signal whose a partial bit stream xe2x80x9c11110xe2x80x9d is repeated is entered into the network apparatus (TDMa), another signal in which the value of xe2x80x9c1xe2x80x9d is continued is inputted into the network apparatus (TDMb) on the reception side. As a consequence, the terminal interface (LS) of the network apparatus (TDMb) would recognize this bit stream signal as the line failure. Thus, there are some possibilities that the above-described failure processing operation would be executed.
As is well known in the field of ATM data communications, in the sending side of an ATM system, bit stream information inputted from a terminal is mapped to the 53 bytes length cell. The 53 bytes cell consists of 5 bytes overhead and 48 bytes payload. The bit stream information is stored in the payload portion.
The receiving side of the ATM system pulls out the 48 bytes length payload from 53 bytes length cell and transmits the payload.
The present invention has been made to solve the above-described problem, and therefore, has an object to provide a simple technique capable of preventing an erroneous line-failure detection by a network apparatus.
A first arrangement according to the present invention is featured by that failure detection data used to detect a failure occurred between network apparatuses and line data with respect to each of terminals connected to the network apparatus are multiplexed to transmit/receive.
In other words, the failure detection data are not set every communication path, but are multiplexed every terminal. It is therefore possible to suppress the probability to a very small value, at which the specific bit stream implying the failure data is generated though no failure happens to occur. As a consequence, it is possible to avoid such an erroneous failure detection notification to the terminal apparatus.
A second arrangement according to the present invention is featured by such a network apparatus to which a plurality of terminal apparatuses are connected, comprising: a plurality of terminal interfaces for receiving lines connected from the plural terminal apparatuses; multiplexing means for bit-multiplexing signals derived from the plural terminal interfaces; failure-occurrence-notifying bit producing means for replacing the multiplexed bit stream signal by a failure-occurrence-notifying bit stream which implies an occurrence of a failure when the failure occurred in a line is detected; and failure-problem processing means for detecting the failure-occurrence-notifying bit stream to thereby process a line failure problem with respect to the terminal apparatus.
The network apparatus of the second arrangement corresponds to a more concrete arrangement of the previously explained first arrangement, and may be applied to either a more concrete TDM transfer system or a more concrete ATM switching apparatus.
A third arrangement according to the present invention is featured by that in the above-described second arrangement, bit operating means is interposed between the multiplexing means and the failure-occurrence-notifying bit producing means, for rewriting the bit stream signal.
Since such a bit operating means is provided, even when a specific bit stream implying an occurrence of a failure (for example, more than 5 bits of value xe2x80x9c1xe2x80x9d are continued in a bit stream) is accidently produced in a multiplexed signal stream, the failure detecting process operation is not executed.
A fourth arrangement according to the present invention is featured by such a network apparatus to which a plurality of terminal apparatuses are connected, comprising: a terminal interface for receiving lines connected from the plural terminal apparatuses, including failure notifying means for notifying an occurrence of a failure to the terminal apparatuses; a line interface connected to an external line, including failure detecting means for detecting a failure of the external line; an actual data path for transmitting actual data appearing in both the terminal apparatuses and the external line; and a failure notification path set to the failure detecting means and the failure notifying means.
As described above, in addition to the actual data path, the failure notification path is set with respect to each of the interfaces. As a result, when the failure happens to occur, the signal state is changed with respect to each of the interfaces, so that the occurrence of the line failure can be notified to the terminal apparatus.
A fifth arrangement according to the present invention is featured by that in the above-explained fourth arrangement, a plurality of terminal interfaces for receiving a plurality of own terminal apparatus lines are provided, and on the other hand, the line interface includes: line condition monitoring means for monitoring the occurrence of the failure with respect to each of the external lines; and a failure notifying unit for notifying the occurrence of the failure to the own terminal apparatus communicated with the external line where the occurrence of the failure is detected by the line condition monitoring means; and failure notification paths are set between the failure notifying unit and each of the plural terminal interfaces.
As a consequence, the occurrence of the failure can be individually notified to such a terminal apparatus connected to the line where the failure happen to occur.
A sixth arrangement according to the present invention is featured by such an ATM switching apparatus interposed between a plurality of own terminal apparatuses and an external line, comprising: a terminal interface for receiving lines connected from the plurality of own terminal apparatuses; an ATM switch for switching a cell between the plurality of own terminal apparatuses and the external line; a line interface for receiving the external line and for including failure detecting means for detecting a failure occurred in the external line; path monitoring means for specifying a path of the external line where the failure happens to occur; failure-notifying cell producing/notifying means for producing/transmitting a failure-notifying cell for notifying an occurrence of a failure to such a terminal apparatus for connecting with the external line where the failure happens to occur in response to information transmitted from the failure detecting means, or the path monitoring means; and output control means for instructing the ATM switch to be turned OFF.
With employment of such an arrangement, also in the ATM network, the occurrence of the line failure can be notified to the terminal apparatus by employing the failure notification cell. As a consequence, the failure erroneous recognition can be prevented, and the failure processing operation with respect to the line failure occurred in the ATM switching network can be readily and firmly carried out.